linux-kernel - Re: [PATCH v7 2/7] mtk-mdp: add driver to probe mdp components

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Message-ID: <ed43d910-d293-fb27-39fe-119836672738@xs4all.nl>
Date:   Tue, 7 Dec 2021 14:02:06 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:     houlong wei <houlong.wei@...iatek.com>,
        Eizan Miyamoto <eizan@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        Yong Wu (吴勇) <Yong.Wu@...iatek.com>,
        "wenst@...omium.org" <wenst@...omium.org>,
        CK Hu (胡俊光) 
        <ck.hu@...iatek.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Yongqiang Niu (牛永强) 
        <yongqiang.niu@...iatek.com>,
        Andrew-CT Chen (陳智迪) 
        <Andrew-CT.Chen@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Minghsiu Tsai (蔡明修) 
        <Minghsiu.Tsai@...iatek.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-media <linux-media@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v7 2/7] mtk-mdp: add driver to probe mdp components

On 12/7/21 1:46 PM, Ezequiel Garcia wrote:
> Hi everyone,
> 
> On Tue, 7 Dec 2021 at 09:37, Hans Verkuil <hverkuil@...all.nl> wrote:
>>
>> On 9/5/21 6:23 PM, houlong wei wrote:
>>> Hi Ezequiel,
>>>
>>> Thank you for your attention to this series of patches. I answer partial of your questions below.
>>> Regards,
>>> Houlong
>>>
>>> On Sat, 2021-09-04 at 20:34 +0800, Ezequiel Garcia wrote:
>>>> Hi Eizan,
>>>>
>>>> Sorry for seeing this series so late.
>>>>
>>>> On Wed, 25 Aug 2021 at 03:35, Eizan Miyamoto <eizan@...omium.org>
>>>> wrote:
>>>>>
>>>>> Broadly, this patch (1) adds a driver for various MTK MDP
>>>>> components to
>>>>> go alongside the main MTK MDP driver, and (2) hooks them all
>>>>> together
>>>>> using the component framework.
>>>>>
>>>>> (1) Up until now, the MTK MDP driver controls 8 devices in the
>>>>> device
>>>>> tree on its own. When running tests for the hardware video decoder,
>>>>> we
>>>>> found that the iommus and LARBs were not being properly configured.
>>>>
>>>> Why were not being properly configured? What was the problem?
>>>> Why not fixing that instead?
>>>>
>>>> Does this mean the driver is currently broken and unusable?
>>>
>>> This series of patches are supplements to another series, please refer
>>> to
>>> https://patchwork.kernel.org/project/linux-mediatek/list/?series=515129c
>>> , which add device link between the mtk-iommu consumer and the mtk-larb
>>> devices. Without that series of patches, the mtk-mdp driver can work
>>> well so far.
>>> But with that series, it seems the device link only can be established
>>> for the device which is registered as a platform driver. That's why
>>> Eizan adds this series of patches to make all mdp components to be
>>> registered as platform drivers.
>>
>> Hold on, so this means that if that iommu device-link series is merged,
>> then the mtk-mdp driver breaks? I posted a PR for that iommu series, but
>> I've just withdrawn that PR until this issue is clarified.
>>
>> Is it only mtk-mdp that is affected by this iommu device-link series, or
>> others as well?
>>
> 
> Like I said before, I think it's a mistake to introduce the component
> framework in V4L2. This whole idea looks like a hack to me.
> 
> If we merge this, then we validate using the component framework
> as a way to avoid fixing things properly.

I agree with Ezequiel.

	Hans